This invention relates to an apparatus and method for minimizing the effect of spillover from the transmitter to the receiver in a same frequency repeater. Spillover refers to a portion of the transmitter signal which is undesirably coupled to the receiver.
A same frequency repeater "SFR" consists of a receiver for receiving a signal at a given frequency and a transmitter for rebroadcasting the received signal at the same frequency. An SFR can be advantageously employed in a communication system to conserve the frequencies or channels required since the SFR reuses the frequency of the received signal by rebroadcasting the received information on the same frequency. By contrast, a conventional repeater receives a signal at a given frequency and rebroadcasts the recovered information at a different frequency. Electrical isolation between the transmitter and receiver in a conventional repeater is more easily attained due to the difference in transmit and receive frequencies.
Isolation between the receiver and transmitter of an SFR at least equal to the gain of the repeater is required in order to prevent oscillation which could result from feedback of the transmitted signal into the receiver, that is, the spillover. Since an SFR may have a gain of a 100 db or greater, isolation becomes an important consideration.
The reception of a first voice encoded signal and a second feedback signal encoded with the same voice information delayed in time by 100 microseconds or more with respect to the first signal will produce distortion. Because the spillover signal from the transmitter of the SFR is time delayed with respect to the received signal, it constitutes a feedback signal which can produce distortion. Thus, it is desirable to minimize the spillover from the transmitter to the receiver of the voice signal carried by the transmitted signal.